1. Field of the Invention
This invention relates to an improved snowmobile drive clutch mounting arrangement and to a snowmobile incorporating such an arrangement.
2. Description of the Prior Art
Conventional snowmobile drive trains incorporate a variable ratio belt drive system having a driving pulley that is directly coupled to the engine crankshaft. The driving pulley acts as a clutch and includes a centrifugally actuated adjusting means through which the drive ratio of the belt drive is varied progressively as a function of the engine speed and the output torque of the driven pulley. Typically, the driven pulley is coupled to a shaft which in turn drives the input member of a chain and sprocket reduction drive the output of which is coupled to one end of the axle of the track-driving sprocket wheels.
This arrangement suffers a number of drawbacks the most significant of which is that the driving pulley is directly exposed to vibrations and movements of the engine, which proves to be detrimental to its efficient operation. Indeed, the efficiency of the belt drive system is adversely affected by any variation in the relative position and/or alignment of the pulleys. A summation of the internal forces present in the belt during operation shows a resulting force vector that tends to pull both pulleys together. The engine being mounted on flexible rubber supports, a displacement of the engine occurs under load which results in a variation of the center-to-center distance of the pulleys together with significant misalignment.
Furthermore, during operation, important reaction forces, resulting from the inertia of the crankshaft and related internal masses being accelerated and decelerated, are generated in the engine housing. These forces result in a displacement of the engine around its supports which further affects the efficiency of the belt drive system.
Typically, a tie-rod is used to restrain longitudinal displacement of the engine housing around its mounts and minimize the consequences on the belt drive operation. However, while to some extent this helps the belt drive situation, it is done at the expense of an increased level of vibrations transmitted to the rider through the frame structure as well as a higher stress level imposed on related structural components which necessitates stronger and heavier construction. To perform satisfactorily, this prior art arrangement necessitates beforehand precise and careful alignment of the engine in the snowmobile frame as well as the correct adjustment of the tie-rod device, which contribute to an increase in the complexity of the assembly operations on the production line.